Wednesday, July 4, 2018

Despite the tools available to combat and control plant
disease, the pathogen which caused the Irish famine continues to destroy
potato crops worldwide

The famine wasn’t that long ago. I can trace my family back to Peter
Lettice and his wife Mary Lowrie who left Ireland in the early 1840s, in
their case for Dundee, Scotland, to avoid starvation. Many people can do the
same. Knowing their names means that the headline figures that get used
in connection with the famine - one million dead and one million
emigrated - become very personal. Those figures get used whenever
anybody talks about the famine, but they make the whole thing anonymous
in a way. It's something that happened to other people and their
families.

The massive global changes brought about by the famine are still
evident in the large number of people claiming Irish heritage in North
America, Australia and elsewhere. At home, the population of the island
of Ireland (approximately 6.5 million in 2016) has only now returned to
pre-famine levels.
Historians can rightly point to many contributing factors and causes
for the famine. Political, social and economic issues all played a role,
but the cause of the crop losses at the heart of the Irish potato
famine ultimately was Phytophthora infestans. This pathogen comes
from a group of organisms called oomycetes and can no longer be
correctly called a fungus. In fact, it’s more closely related to the
brown algae.

The ‘father’ of plant pathology, Anton de Bary,
was the first to demonstrate experimentally that the pathogen caused
the disease we now know as late blight and de Bary coined the name Phytophthora, meaning "plant-destroyer". English botanist Rev. Miles Berkeley
had first observed that late blight was "the consequence of the
presence of the mould, and not the mould of the decay" 15 years earlier (Journal of the Horticultural Society of London, 1846).

Phytophthora is an appropriate moniker. Symptoms of the
disease include blackish lesions on the leaves and purple-brown lesions
on the surface of the tubers themselves. When the disease is advanced,
the tubers are rotten inside and there is a distinctive odour which must
have struck fear into the heart of poor subsistence farmers all over
the country during the famine.

As any potato grower will tell you, late blight of potatoes has not
gone away. It remains the most economically destructive of all potato
diseases worldwide. Typically, commercial potato growers in Ireland use
between 15 and 20 applications of fungicide to control the pathogen
every year and there are no commercially-viable resistant varieties
available. 170 years after the famine, our potato crop is still as
vulnerable as ever to destruction caused by Phytophthora. The difference now is the availability of chemical control options to keep the worst of the losses at bay.

Globally, many crops are vulnerable to diseases that have the potential to cause devastating losses. For example, rice blast fungus (Magnaporthe oryzae) is the most destructive disease of rice, a staple foodstuff that feeds half the world’s population. Diseases of cereals like Puccinia and Fusarium
are a threat that require constant vigilance and we are regularly
reminded that the much-loved and economically important Cavendish
variety of banana (that’s the banana you had for lunch) is on the brink
of extinction due to Panama disease caused by Fusarium oxysporum.

A major problem is our over-reliance on a small number of crops for
much of the world’s food supply. Just 15 crop plants account for 90
percent of the world’s food with maize, wheat and rice accounting for
over 50 percent of the world’s caloric intake (UN FAO). If even one of
the top ten crops were to fail, the consequences could be catastrophic, especially for developing countries.
Increasingly though, we are running to stand still with a lot of the major diseases. Much like the Red Queen in Lewis Carroll’s Through the Looking-Glass, keeping one step ahead of emerging and evolving plant pathogens "takes all the running you can do, to keep in the same place".

In this context, it’s more important than ever that we are using all
of the tools available to us to combat and control plant disease. That
means an integrated approach to pathogen and pest management where one
tool such as chemical control is not over-used. Such reliance on one
control method runs the risk of forcing the pathogen to evolve to
overcome the control measure, rendering it useless.

One of the tools that will certainly be in that toolbox is the
development of resistant varieties. However, in the case of late blight,
we’ve yet to breed a commercially-viable, fully blight-resistant
potato. That’s not to say it’s impossible: Sarpo Mira, Sarpo Axona and Blue Danube
are all potato varieties that are very resistant to late blight but
they have not been commercially successful outside of the organic
market.

Luckily, help is at hand in the form of modern plant biotechnology
which has the capacity to quickly develop blight resistant potato
varieties as well as resistant crops to various other diseases) A major
problem with conventional potato breeding is the difficulty in crossing
domesticated varieties with their disease-resistant wild relatives.
Genetic transformation has overcome that problem by transferring a
potato gene for resistance from wild to cultivated varieties. Such
varieties were grown successfully in Ireland in recent years.

Gene-editing technology will allow even more precise changes to be
made to plant genomes with the goal of introducing resistance for a host
of important crop diseases. Whatever our personal views on such
technologies, there is no doubt they will be an integral part of
maintaining global food security and preventing future famines.

Recently, Ireland was named the most food-secure nation in the world.
That’s an amazing turnaround, even if it has taken 170 years. In light
of our remarkably journey from famine to world leaders in food security,
surely there is a moral imperative on us to support other countries to
boost their food security - and to advance the science that will prevent
similar famines from happening to other countries in the years to come?

It's just a little bit of science!

Welcome to Communicate Science.I'm a plant scientist, so expect lots of plant-related posts but also lots on science in general and science communication.Enjoy!

Contact: communicatescience1@gmail.com

All content, unless otherwise stated, is copyright of Communicate Science and should not be used without prior consent.Opinions expressed on this blog represent my own views and not those of my employer. Any comments on posts represent the opinions of visitors.

Wade through the scrivenery

Subscribe for Free

Tweet, Tweet

Bits and pieces on the blog

This is me

I'm passionate about the need to enthuse, inform and engage everyone in society about science.
I'm a full-time researcher and lecturer and a part-time blogger. I'm interested in all things to do with science. In particular, education and communication of science - especially biology.
This blog represents my personal views.